Instagram has defended its guidelines on nudity after Scout Willis staged a topless protest in New York.

The 22-year-old daughter of Bruce Willis and Demi Moore posted pictures of herself walking the streets without a top or bra on Twitter.

Willis' Instagram account was suspended when she shared a photo featuring two topless women.

She has been backed by singer Rihanna, who reportedly left the photo-sharing website herself after some of her own racy photos were removed from the site.

Instagram said its guidelines put "limitations on nudity and mature content" and almost all of the photos removed from the site follow complaints by other users.

A spokeswoman said: "We try hard to find a good balance between allowing people to express themselves creatively and keeping Instagram a fun and safe place.

"Our guidelines put limitations on nudity and mature content. Once content is reported to us, we review it and remove if it violates our policies."

Image:Kevin Systrom is the co-founder of Instagram

Instagram's terms of use state that users may not post "violent, nude, partially nude... pornographic or sexually suggestive photos or other content via the service."

Alongside Willis' topless protest pictures, she tweeted: "What Instagram won't let you see. FreeTheNipple" and "Legal in NYC but not on Instagram".

In a blog post on the xoJane website, Willis explained the reason for her protest, claiming the site deleted her account when she posted a photo of herself in a sheer top and a photo of a jacket she made that featured two topless friends.

"My situation was in no way unique," she wrote in her blog.

"Women are regularly kicked off Instagram for posting photos with any portion of the areola exposed, while photos sans nipple - degrading as they might be - remain unchallenged.

"So I walked around New York topless and documented it on Twitter, pointing out that what is legal by New York state law is not allowed on Instagram.

"What began as a challenge to Instagram and its prejudiced community guidelines became an opportunity for dialogue."

Willis has said that for every "nasty" comment she had received following her protest, there were "10 more of support, appreciation, and empowerment".